1- after creating a new wallet using 1 wallet with seed and other with master pub key + attacking trezor device, now when I go to send button and hit sign in my trezor sighing pops up and when I sign it from trezor device it just simple send payment without asking me to sign from the 2nd and from the 3rd owners?
A 2-of-3 multi-sig wallet requires two signatures to make a transaction. Usually, a 2-of-3 multi-sig wallet is split across three wallets, so that each wallet contains only a single set of private keys. With such a set up, to make a transaction you must first sign it from one wallet with one private key, then move it to one of the other two wallets to sign it with a second private key. Once it has two signatures, it can be broadcast.
However, you can also set it up so that a single wallet contains more than one set of private keys. If you have a wallet file which contains both an Electrum seed and can sign from your Trezor wallet, then this wallet will be able to provide the necessary two signatures on its own.
2- in future what if these 3 owners (2 Computer wallets + 1 Hardware device) get apart ... how can they restore this multiple wallet if they don't have complete 3 wallets on hand? let's say I lose my hardware device but still have 2 wallets with seed and master .. how can I even restore my wallet without hardware ..? on 3/2 wallet creation it ask must to restore from all three otherwise it won't work ..?
If you lose your hardware device, then you will still be able to recover your multi-sig wallet by using the seed phrase from your hardware device which you should have backed up.
To restore a 2-of-3 multi-sig wallet you either need all three seed phrases, or two seed phrases plus the missing master public key.
3- I tried to restore my 3/2 wallet by using 2-2 multisig wallets using 1seed + 1master (without hardware)... and seems like it doesnt' restore the actual wallet .. it is just a new wallet of 2-2... how can we restore these kind of wallets ..?
That's not how it works. Once you've created a 2-of-3 multi-sig, it will always be a 2-of-3 multi-sig. You cannot convert it to 2-of-2 and you cannot "partially" restore it. You will always need all three components to restore it.
4- Multisig only works for Bitcoin. What if I can use a hardware Trezor device which has many other crypto assets like ethereum and other assets, would my other assets would stay on the same hardware wallet ..? I mean whenever I need to transfer/access Bitcoin I use multiple using electrum .. and when I need to access other assets I use trezor suit to access them .. is it possible to use one device for two purposes ..?
Yes, your Trezor should be able to simultaneously support a bitcoin multi-sig wallet and altcoin single-sig wallets using the same seed phrase.